M116A3 Build

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Re: M116A3 Build

Postby John61CT » Sun Jan 23, 2022 3:41 pm

SoC% is never better than a guesstimate, within 5-8% is the best you should expect.

the only exceptions being at **your** definition of 100% when you should reset the BM, ideally whenever you get there.

If you go weeks never getting there, great for cell health, but the BM will drift, a lot.

And at **your** definition of LVC to protect the battery, which IMO should be called 0%

For longevity's sake, only allow the latter to be approached in an emergency, staying above 20% SoC can triple the bank's life cycles.

You already have a "Full definition" good for longevity but the other key is, don't let the bank sit there for long, bit of a balancing act there.
Last edited by John61CT on Sun Jan 23, 2022 3:57 pm, edited 1 time in total.
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Re: M116A3 Build

Postby John61CT » Sun Jan 23, 2022 3:48 pm

> I wonder how I can get a 100% charge out of the system?

Sorry, do not understand the reason for that desire?

And again, you define what 100% means

There is no Absolute definition with precision

Here are four examples, with my editorial comments

A. nameplate Ah rating of the pack will vary from actual tested Ah capacity

B. spec sheet maximum stop-charge voltage let Absorb current taper to 0A, call that "theoretical / vendor 100%" SoC level (should not be used in practice, consider it destructive)

C. 3.45V taper CV stage to 0.03C (or 0.05C) and Stop, "actual usage 100% Full, for regular testing or BM calibration" (requires a decent charge rate, say >0.1C)

D. 3.xxV and Stop, Bulk / CC-only no-CV "daily usage cycling Full" (should vary, depends on charge rate)
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Re: M116A3 Build

Postby John61CT » Sun Jan 23, 2022 3:55 pm

So if longevity is the goal, capacity sacrifice is required, basically just accept those top and bottom Do-Not-Approach shoulder areas are not available (outside emergencies)

And, the stop-charge formula for normal cycling will vary by context, source type and current rate.

Resetting the BM at 100% for daily use does not demand a precise calibration point, as with protocol C above.

The point is to have reasonable feedback to start shutting down non-critical loads in a solar - only scenario

or to fire up the genset if available
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Re: M116A3 Build

Postby lfhoward » Sun Jan 23, 2022 5:42 pm

I think I get what you’re saying, that “full” does not mean the same as 156 amp hours (the maximum capacity of my battery). The level I call “a full battery” would be what I want to set as the normal point at which charging stops (13.8 volts in this case). That level of “full” would trade some amp hours of capacity for long battery life. I am on board with that trade off. So basically, my battery was full at noon today when it went into absorption mode at 13.8 volts. Even though the battery monitor indicated some amp hours were left on the table and capacity was at 89%, it is basically 100% for my purposes. I can synchronize the battery monitor to 100% next time we hit 13.8 volts / absorption, and not worry about bringing the battery up any higher.

Let me know if my summary above makes sense, based on your experience & understanding of how these systems work. Thanks!
My off-road camper build on an M116A3 military chassis:
http://www.tnttt.com/viewtopic.php?f=50&t=62581
Tow vehicle: 2008 Jeep Liberty with a 4 inch lift.
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Re: M116A3 Build

Postby lfhoward » Mon Jan 24, 2022 2:09 pm

I manually synchronized the battery monitor to 100% when the voltage reached 13.8 today and the charge controller went into absorption and later float. This level is now "full" from the perspective of my usage.
My off-road camper build on an M116A3 military chassis:
http://www.tnttt.com/viewtopic.php?f=50&t=62581
Tow vehicle: 2008 Jeep Liberty with a 4 inch lift.
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Re: M116A3 Build

Postby John61CT » Mon Jan 24, 2022 4:18 pm

lfhoward wrote: 156 amp hours (the maximum capacity of my battery)


According to what test specs? That number will vary greatly depending on the specs of the CC discharge test: Start V, end V, and C-rate.

There is no "objective" measure. Cheap-chinese vendors will use say

3.65V to 2.50V, at a CC rate of 0.05C

and then marketing bumps the Ah result up a bit.

Top notch vendors actually deliver more than rated, sometimes by 10-15%!

...

> The level I call “a full battery” would be what I want to set as the normal point at which charging stops (13.8 volts in this case).

Voltage alone does not specify SoC%

That will also vary, based on

CC-only, stop immediately hitting 13.8V The resulting Ah capacity will then vary by the C rate.

or holding CV / Absorb until current trails down to an endAmps spec, 0.2C will differ a bit from 0.05C

I realize all these details may seem obscure, even irrelevant to many, I only offer them for those who want to understand...


> So basically, my battery was full at noon today when it went into absorption mode at 13.8 volts.

OK then yes, you got it, that is when you let the BM know you are at 100%

And if you trust that 156Ah and want longevity, leave at least say 26 in at the botton

so do not draw down more than 130Ah before recharging.

Also using say 3.10V as an LVC point, whichever you hit first.
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Re: M116A3 Build

Postby lfhoward » Mon Jan 24, 2022 5:11 pm

Thanks for the reflection, John. Sounds like we have a plan.

The 156 Ah statistic is from the labeling, but I also capacity tested the cells at 0.2 C after top balancing and got slightly more.

Not discharging past -130 sounds like good advice as well.
My off-road camper build on an M116A3 military chassis:
http://www.tnttt.com/viewtopic.php?f=50&t=62581
Tow vehicle: 2008 Jeep Liberty with a 4 inch lift.
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Re: M116A3 Build

Postby lfhoward » Fri Jan 28, 2022 8:46 pm

We have a winter storm warning for tonight. The battery heaters are OFF because the solar panel will be covered in 5-9 inches of snow tomorrow morning. I’ll have to go to where I keep the trailer to clean the snow off. The battery can run the 8 watt load of the VRM Raspberry Pi’s for 2028 watt hours/8 watts = 253.5 hours. That’s just about 10 days (closer to 9 days if leaving a 10% buffer at the bottom). So, got to visit the trailer with my snow brush sometime next week, lol. So far on a cold sunny day in January, I have seen the roof panel capture 660 watt hours, so it can recover the battery quickly.
My off-road camper build on an M116A3 military chassis:
http://www.tnttt.com/viewtopic.php?f=50&t=62581
Tow vehicle: 2008 Jeep Liberty with a 4 inch lift.
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Re: M116A3 Build

Postby featherliteCT1 » Sat Jan 29, 2022 4:53 pm

It is like tending to a baby ... thinking about it all the time! :thumbsup:
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Re: M116A3 Build

Postby lfhoward » Sat Jan 29, 2022 5:38 pm

featherliteCT1 wrote:It is like tending to a baby ... thinking about it all the time! :thumbsup:

Ha! Yes, true at this point. Once I install that timer to run the battery heater during early morning and daylight hours, it will be pretty autonomous.
My off-road camper build on an M116A3 military chassis:
http://www.tnttt.com/viewtopic.php?f=50&t=62581
Tow vehicle: 2008 Jeep Liberty with a 4 inch lift.
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Re: M116A3 Build

Postby John61CT » Sat Jan 29, 2022 8:18 pm

For long term storage after the honeymoon period, personally I'd bring the pack home and just keep it isolated at storage voltage.

Unnecessary cycling, risk of something failing...
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Re: M116A3 Build

Postby lfhoward » Wed Feb 09, 2022 5:05 pm

I installed a programmable timer on the battery heater circuit, so that the heater’s thermostat would only be energized from 6 am to 2 pm (when sunlight is available to recharge). It has made the battery’s charging system completely autonomous.

Image

http://timers.shop/6V-28V-10-Amp-Timer-Wi-Fi-configurable-via-phone_p_44.html

This timer has more than 30 different modes. If I am feeing like taking on a challenge I can even program the nearby Raspberry Pi to be able to trigger the timer and control it remotely. But right now it is set up as a simple timer only.
My off-road camper build on an M116A3 military chassis:
http://www.tnttt.com/viewtopic.php?f=50&t=62581
Tow vehicle: 2008 Jeep Liberty with a 4 inch lift.
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Re: M116A3 Build

Postby John61CT » Wed Feb 09, 2022 11:20 pm

Lots of ideas...

Good stuff
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Re: M116A3 Build

Postby bdosborn » Sun Feb 13, 2022 11:40 pm

lfhoward wrote:I installed a programmable timer on the battery heater circuit, so that the heater’s thermostat would only be energized from 6 am to 2 pm (when sunlight is available to recharge). It has made the battery’s charging system completely autonomous.


I've been commissioning the van electrical system and digging into the relay settings of the Cerbo GX. It has two relays built in that that you would have found handy. One can be used for generator control so it has time of day and SOC settings that would function the same as the timer you added. The other relay can be turned on and off by a Cerbo GX temperature sensor, ideal for a battery heater. I plan to use the temperature controlled relay to control my battery heaters via a 12V Bosch type relay. I also plan to use the relay to disable the inverter/MPPT/DC DC chargers at 2C. The temperature graph and relay state info shown in the VRM is pretty spiffy:

Image

The Raspberry Pi has GPIO pins for a relay that can be used to control a generator too (according to the GitHub Venus description but its a bit vague on what pins they are), it would let you adjust your battery timer remotely via the Venus software. You'd need to use an opto-isolated relay to connect to the Pi GPIO.
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Re: M116A3 Build

Postby lfhoward » Sat Mar 19, 2022 9:12 pm

I got a few odds and ends finished with the trailer battery electrical today.

1. I installed new cooling fans from pishop.us (https://www.pishop.us/product/highpi-pro-5v-cooling-fan/) that I programmed to turn on to cool the Raspberry Pi’s once the CPU temperature reached a certain threshold. (Set to turn on at 65 degrees C, as the CPU becomes throttled at 85 degrees C) These new fans replaced noisy fans that were just always on 24/7. The new ones have 3 wires, the old ones just two. Not being on all the time will conserve a little bit of battery energy, and the fans should last longer before the bearings give out.

2. I installed a trigger wire from a GPIO pin on the Pi to control my battery heater timer (http://timers.shop/6V-28V-10-Amp-Timer-Wi-Fi-configurable-via-phone_p_44.html), and programmed the raspberry pi to turn it on at 6 am and off at 2 pm. This beats the timer’s built-in clock which drifted over time and had to be manually reset once a week. It is easy to put the voltage trigger command in the Pi’s crontab function. I can also call the function remotely or change the on-off timing remotely if I want. The timer is now a highly customizable 10 amp relay like Bruce described above. Of course we hit a warm spell and the battery heater will not be needed all week (is winter over?), so I turned it off to save a watt.

3. I started (unsuccessfully so far) to install the dbus-serialbattery mod (https://github.com/Louisvdw/dbus-serialbattery) that allows the Venus OS to see and control my battery’s Overkill BMS. Looks like maybe I didn’t have the wires hooked up properly because the BMS did not show up as a battery monitor on the Venus/VRM and the battery voltage started to fluctuate and was read incorrectly by the Venus. I disconnected the serial cable and un-enabled the dbus software temporarily, because I didn’t have time to fully work out the proper wiring/programming yet. More to come on this because I haven’t given up. Has anyone here had success setting this up? (Bruce, have you tried this with yours?)
My off-road camper build on an M116A3 military chassis:
http://www.tnttt.com/viewtopic.php?f=50&t=62581
Tow vehicle: 2008 Jeep Liberty with a 4 inch lift.
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